For a number of years it has been known that various microorganisms produce secondary metabolites exhibiting biological activity so as to be useful as pesticides for controlling diseases and pests.
Although progress has been made in the field of identifying and developing biological pesticides for controlling various diseases and pests in plants and animals of agronomical and horticultural importance, most of the pesticides in use are still synthetic compounds that are difficult to decompose in nature and have a broad spectrum of activity.
In the last decade or so there has been an increasing concern for the impact of such pesticides on the environment and the ecosystems surrounding farmlands, and consequently there exists an outspoken need for pesticides that are more specific in their activity, and are readily degradable in the natural environment.
Natural products provide an alternative to synthetic fungicides and insecticides in that they may have another mode of action, may be more biodegradable and safer in the environment.
Several compounds have been previously isolated from the genus Pyrenophora. The Aspergillomarasamines, including Toxin A (below), are a series of compounds derived from several genera of fungi including Pyrenophora. These compounds are toxic to higher plants and are widely distributed in fungi. (Physio. Plant Path., Vol. 14, pp. 41-46, 1979).
Another series of compounds isolated from a number of genera including Pyrenophora are the Ophiobolins. A report of these phytotoxic and antimicrobial compounds from P. teres has not previously been made. (Proc. Natl. Acad. Sci. USA, Vol. 84, pp. 3081-3085, 1987). Pyrenolide compounds have been isolated from P. teres. (Agric. Biol. Chem, Vol. 44, pp. 2761-2762, 1980). However, their biological activity spectrum includes antifungal activity but no insecticidal activity.
Compounds reported from the genus Pyrenophora are the following: ##STR1##
It is, therefore, an object of the present invention to provide novel fungicidal and insecticidal compounds which originate from natural sources or are direct derivatives of such compounds and which confer protection for plants against harmful fungi and insects.